> 1. What percentage of Android devices download apps exclusively from Play? They don't say. I, for one, have quite a few not so technical friends who sideload stuff.

I also have an anecdote to share. The only app I've sideloaded and helped others sideload was the one I created myself. Out of 10 teenagers who are the most probably to tinker, 0 of them usually install apps from sources outside of the play store.